The 2-PHASE.TM. (a trademark of the Xerox Corporation) extraction process provides a method and apparatus for removing chemicals and other undesirable substances from a contaminated area of the ground. Generally speaking, an extraction tube or the like is placed with the affected area and a vacuum is applied to draw soil vapors and groundwater into the well. Application of the vacuum to the soil vapor initiates a high velocity vapor stream at the bottom of the well, entraining the contaminated groundwater and soil gas. Both phases are then lifted to the surface as a single two-phase stream. The liquid and vapor are then separated, and each phase is treated to remove contaminants. Such processes are disclosed in U.S. Pat. No. 5,464,309, U.S. Pat. No. 5,441,365, U.S. Pat. No. 5,358,357, U.S. Pat. No. 5,197,541, U.S. Pat. No. 5,172,764, and U.S. Pat. No. 5,050,676, all assigned to Xerox Corporation, Stamford, Conn.
Contaminants can be found in subsurface soil and groundwater, in the liquid or vapor phase. They can exist as discrete substances, or they can be mixed with and/or dissolved in groundwater and soil vapors. Such contaminants can be found in the vadose zone (the unsaturated layer that lies between the surface of the earth and the water table), at the interface between the vadose zone and the water table, and in the saturated zone below the water table.
Many industrial and commercial facilities and waste handling and disposal sites contain soil and groundwater contamination. A variety of techniques have been used for removal of contaminants and remediation of affected media. One common technique entails the excavation and off-site treatment of the soil. Another technique entails saturating the contaminated soil with water in situ, causing the contaminants to be leached slowly from the soil by the water. The contaminated water can then be removed.
One very effective technique for removing chemicals from a contaminated area of the ground involves removal of soil contaminants using the 2-PHASE.TM. extraction process. The process generally involves providing a borehole in the contaminated area, placing an extraction well inside of the borehole, and applying a vacuum to the well such that vapors and liquid can be drawn from the soil. The liquid and vapor are transported to the surface simultaneously as a two-phase stream. After it reaches the surface, the liquid-vapor stream is separated into two independent streams. Each stream is then treated for removal of the contaminants.
Various types of contaminants may be removed from the ground using a process such as two phase extraction. An effluent stream may include organic and inorganic substances, as well as those that are soluble, insoluble, volatile, and non-volatile. The various classes of contaminants are subjected to post-extraction treatment to remove them from the vapor or liquid in which they reside. Suitable post-extraction treatment processes for contaminant removal typically, but not necessarily include filtration, adsorption, air stripping, settling, flocculation, precipitation, scrubbing and the like.
As the two-phase stream is extracted from the ground, application of the vacuum causes many of the liquid volatile organic contaminants to be transformed to vapor phase contaminants, but measurable amounts of contaminants can remain in the liquid phase. Effective methods have been developed for treating the vapor portion of the stream to remove its remaining contaminants. However, treatments that have been developed to remove contaminants from the liquid portion of the effluent have not been as cost effective. Thus, it is desirable to provide an arrangement for transferring these volatile organic contaminants from the liquid phase to the vapor phase prior to post-extraction treatment. This will allow the effluent to be treated in the most efficient manner, resulting in maximum contaminant removal at relatively low cost.
The following disclosures may be relevant to various aspects of the present invention:
U.S. Pat. No. 5,441,365 to Duffney et al. issued Aug. 15, 1995 discloses an apparatus and process for extracting contaminants from a combined vapor-liquid stream. The gas component of the stream is cooled and heated several times to condense and remove volatile organic compounds. It is then re-combined with the rest of the discharge, subjected to further treatment, and released into the environment.
U.S. Pat. No. 5,358,357 to Mancini et al. issued Oct. 25, 1994 discloses a process for removing contaminants from a contaminated area of the ground having a vadose zone and a water table, which comprises providing a borehole in the contaminated area to a depth below the water table; placing in the borehole to a depth below the water table a perforated riser pipe inside of which is situated a vacuum extraction pipe with a bottom opening situated within the perforated riser pipe, said vacuum extraction pipe containing groundwater prior to application of a vacuum thereto, said vacuum extraction pipe having at least one gas inlet situated below the groundwater level in the vacuum extraction pipe; while introducing a gas into the riser pipe, applying a vacuum to the vacuum extraction pipe to draw gases and liquid from the soil into the perforated riser pipe and from the riser pipe into the vacuum extraction pipe and transport both the gases and the liquid to the surface as a two-phase common stream; introducing a gas into the vacuum extraction pipe at a level below the groundwater level in the vacuum extraction pipe to initiate two-phase flow within the vacuum extraction pipe; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and separately treating the separated liquid and gas streams.
U.S. Pat. No. 5,143,607 to Bernhardt issued Sep. 1, 1992 discloses a arrangement for driving volatile impurities from groundwater using air or another gas. A shaft adapted to extend to a groundwater region has at least locally a water-permeable wall formed as another wall and limiting at least partially an air receiving chamber communicating with an outside air, a ventilator communicating with the shaft for producing a negative pressure and aspirating air from a shaft portion located above a groundwater level. A pipe extends in the shaft to an area under the groundwater level so as to form the air receiving chamber and to provide communication to the outside air. The pipe has an inner end region surrounded with nozzle openings, a screening sleeve arranged concentrically relative to the pipe and at least partially covering the end region of said pipe provided with said nozzle openings. The screening sleeve is supported displaceably relative to the pipe and sealed relative to the pipe and a floating body coupled with the pipe.
U.S. Pat. No. 5,122,165 to Wang et al. issued Jun. 16, 1992 discloses a process system and apparatus for removal of toxic volatile organic compounds (VOCs), volatile inorganic compounds (VICs) and surfactants from a contaminated liquid stream, more particularly groundwater, by a combination of pH adjustment, chemical reaction, ultraviolet reaction, gas stripping, scrubbing, adsorption and regeneration is described. This process system involves liquid pumping; liquid treatment in an enclosed dispersed gas stripping chamber; gas purification by a foam collector, a wet scrubber and a self-generative gas-phase granular activated carbon (GAC) contactor; and recycling of GAC-purified gas for further liquid treatment by dispersed gas stripping. The process system is extremely cost-effective for removal of VOCs, VICs, and surfactants, and eliminates the problem of secondary gas contamination caused by conventional air stripping towers.
U.S. Pat. No. 5,116,515 to Selesnick issued May 26, 1992 discloses a process and apparatus for removing volatile organic contaminants from vadose soil areas. The process comprises drawing air through recovery probes that have been positioned in the soil. A blower is then activated at intervals to draw gaseous vapors from the ground above the underground water level. The gases are collected in a water separator tank where they are separated from the accidentally collected liquids. The gases are then passed through a filtration device for cleaning.
U.S. Pat. No. 5,050,676 to Hess et al. issued Sep. 24, 1991 discloses a process for two phase vacuum extraction of contaminants from the ground involves vacuum withdrawal of liquid and gaseous phases as a common stream, separation of the liquid and gaseous phases, and subsequent treatment of the separated liquid and gases to produce clean effluents. Two phase vacuum extraction employs a single vacuum generating device to remove contaminants in both the liquid stream and soil gases through a single well casing.
U.S. Pat. No. 4,966,654 to Carberry issued Oct. 30, 1990 discloses a system for removing volatile hydrocarbon contaminates from both water and moisture-ladened air. In detail the invention comprises a stripping system preferably a steam stripping system, for mixing the contaminated water with steam, at below atmospheric pressure, providing clean water for reuse and contaminated steam and vaporized hydrocarbon contaminates. A first condenser receives the contaminated steam and vaporized hydrocarbon contaminates and condenses, at below atmospheric pressure, a portion of the vaporized contaminates and a portion of the contaminated steam into contaminate water. A second condenser thereafter further condenses the steam and hydrocarbon vapor. A gravity separator thereafter receives the contaminated water from the first and second condensers and the uncondensed steam and hydrocarbon contaminates from the second condenser and provides outputs comprising: separated contaminated water for recycling; condensed hydrocarbon contaminates for reprocessing; and passes the uncondensed hydrocarbon contaminates to activated charcoal absorbers. The contaminated moisture-ladened gas is passed through a third condenser which produces contaminated water which is recycled to the steam stripping system and the remaining uncondensed hydrocarbons are passed through the activated charcoal absorbers.
U.S. Pat. No. 4,943,305 to Bernhardt issued Jul. 24, 1990 discloses an aerating apparatus or aerator for expelling the impurities from groundwater, especially for ground water under an overpressure, in which the impurities are expelled by generating a partial vacuum in an aeration shaft in the vicinity of ground water to be purified and by feeding fresh air below the water level in the aeration shaft, the aeration shaft is closed on its upper end with a pressurized receiving chamber. The pressurized receiving chamber permits fresh air to be brought in at an air pressure balancing the ground water pressure. Moreover a vacuum generator producing the partial vacuum is located in the pressurized receiving chamber.
All of the references cited herein are incorporated by reference for their teachings.
Accordingly, although known apparatus and processes are suitable for their intended purposes, a need remains for processes and apparatus for pre-treating contaminated liquids and gases obtained from soil with increased efficiency. Further, there is a need for processes and apparatus for enhancing the concentration of volatile contaminants in the gas phase of an effluent mixture, thereby decreasing the concentration of contaminants in the liquid phase.